Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $201.75   10.666%   $223.2687   $223.27   $223.25   $223.30  
  Purchase #2 $108.67   13.727%   $123.5871   $123.59   $123.60   $123.60  
  Purchase #3 $150.95   8.316%   $163.503   $163.50   $163.50   $163.50  
  Purchase #4 $90.73   6.560%   $96.6819   $96.68   $96.70   $96.70  
  Purchase #5 $208.43   12.641%   $234.7776   $234.78   $234.80   $234.80  
  Purchase #6 $14.92   13.637%   $16.9546   $16.95   $16.95   $17.00  
  Purchase #7 $210.79   13.156%   $238.5215   $238.52   $238.50   $238.50  
  7 purchase totals = $986.24       $1,097.2944   $1,097.29   $1,097.30   $1,097.40